The liquid phase hydrogenation of coal can be carried out by mixing coal with a solvent which acts as a hydrogen donor and then heating the mixture to a temperature between about 400.degree. C. and 500.degree. C. under hydrogen pressure, in the presence of a catalyst.
Numerous catalysts have been proposed for this reaction. Among these are catalysts based on noble metals (for example cobalt or nickel together with molybdenum or tin) that have the advantage of being relatively active. These catalysts are, however, expensive. Moreover, it is difficult to recover them from the hydrogenation residue.
Iron catalysts have been proposed which have the advantage of being less expensive than the noble metal catalysts. These iron catalysts are, unfortunately, less active than other catalysts, and they must be used in large amounts in the hydrogenation mixture. This results in many disadvantages, such as the danger of blockage of the reactor and of the pipelines surrounding the reactor, an increase in the corrosion of the valves in the reaction system, and an increase in the amount of material to be handled and to be heated.